Injection valve

ABSTRACT

A method for producing a filter element includes forming longitudinal ducts extending between upstream and downstream surfaces of the filter element, and installing a heating element for heating regions of walls of the ducts along longitudinal extent of the walls. The filter element is arranged inside an injection valve of an internal combustion engine.

BACKGROUND AND SUMMARY OF THE INVENTION

The present application is a division of patent application Ser. No.09/770,293, filed Jan. 29, 2001, now U.S. Pat. No. 6,616,066, the entiredisclosure of which is incorporated herein by reference. Priority isclaimed based on Federal Republic of Germany Patent Document Nos. 100 03935.9, filed Jan. 29, 2000, and 100 53 583.6, filed Oct. 28, 2000, thedisclosures of which are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an injection valve for internal combustionengines, with a filter element arranged on the inside of the injectionvalve in the fuel flow of the latter and having ducts for the fuel.

Patent literature (WO 93/02284, EP 0472 417 A1, U.S. Pat. No. 5,050,569,U.S. Pat. No. 5,758,826 or U.S. Pat. No. 5,179,927) discloses a seriesof injection valves of this type which are also provided for the heatingof fuel prior to injection into the combustion space of internalcombustion engines. However, all the approaches used here for heatingthe fuel are distinguished by a comparatively large mass to bepreheated. They therefore all have a high energy consumption and a longresponse time>60 s.

An object of the invention is to develop an injection valve and amethod, by means of which, particularly when the engine is cold,improved mixture formation and as small a fraction as possible of CH inthe exhaust gas during the starting phase can be achieved.

This object of the invention is achieved by providing an injection valvefor internal combustion engines, with a filter element arranged on theinside of the injection valve in the fuel flow of the latter and havingducts for the fuel, wherein the filter element is designed as athroughflow heating element, and wherein the walls of the throughflowducts are capable of being heated, at least in certain regions, alongtheir longitudinal extent. The invention is distinguished by anextremely reduced thermal mass of the filter element which is embodiedas a heating element. As a result, the response time for heating isreduced to a few seconds and the peak energy consumption is minimized(200 W→20 W).

Thus, in particular, by virtue of the use of semiconductor material suchas silicon as heater material and the shaping of the latter by meansfound in microsystem or semiconductor technology such as anisotropicetching, it is possible to produce very large surfaces (innersurface>300 cm² in the case of a heater area of 1 cm²) for the exchangeof energy between the fuel and the heating element. According to anembodiment of the invention, the semiconductor material isnoncrystalline. The semiconductor material may also include conductivealuminum.

PTC resistors have hitherto been used as heating elements and theymaintain a fixed surface temperature of the heater without externalregulation. On account of this, it has not been possible hitherto toregulate the heating capacity in an active way. This means that it isimpossible to regulate the heating capacity, for example so as to adaptto varying fuel properties or quantities.

By contrast, the present invention makes it possible to have rapidresponse times in the seconds range, so that the heating element can bedesigned with out the disadvantage of additional waiting times.

Furthermore, the heating elements according to the invention are sosmall that they can be integrated into a conventional injection valve,specifically without the external dimensions of the injection valvehaving to be changed.

In order to measure the heating function of a filter element accordingto the invention, heptane, on the one hand, and water, on the otherhand, were conveyed through the latter. The respective filter elementhad a diameter of approximately 10 mm. The diameter of a web between twoadjacent ducts amounted to approximately 20 μm, the duct length toapproximately 300 μm and the duct diameter to approximately 90 μm.

In this filter element, it was possible to achieve a maximum throughflowof about 870 l/h at a water pressure of 6 bar. The achievable heatingcapacities were between 13 and 35 Watt.

With this set of parameters and a throughflow of about 2 l/h, it waspossible for the liquid conveyed through to be heated by 30 to 50° C.within 10 s to 20 s.

Surprisingly, despite its crystalline and therefore brittle material,the filter element did not exhibit any impairments in the case offluctuations in the pressure of the liquid conveyed through.Consequently, also surprisingly, the mechanical stress on the materialof a filter element according to the invention due to a slight pressuredrop in a duct is uncritical and, in general, negligible.

Furthermore, local overheating possibly occurring within a duct can beignored, since the heat in the filter element is distributed veryquickly on account of the high thermal conductivity of the semiconductormaterial.

Expediently, an inventive, in particular semiconducting filter elementcan be used not only for heating, but also as a temperature sensor. Forthis purpose, preferably, the electrical resistance of the filterelement developed as a heating element is determined (preferably when itis not heated) and is compared with an (in particular, predetermined)characteristic curve representing the temperature and/or resistanceprofile.

The relation between the fuel temperature and the electrical heatingcapacity makes it possible, by intelligent evaluation, to obtain furtherinformation, for example on the boiling point of the fuel andconsequently, inter alia, the quality of the latter.

This possibility is based, inter alia, on the fuel forming bubbles atthe boiling point. As a result of this bubble formation, thetransmission of heat from the filter element into the fuel is lower.Consequently, the filter element is subject to greater specific heating,which can be detected not only from a certain temperature rise, but, forexample, also from a significant change in the current/voltagecharacteristic curve and therefore also in the delivered heatingcapacity.

In this case, that is to say at the start of bubble formation due to theevaporation of the fuel, the measured heating capacity, preferablydetermined from the current/voltage graph, deviates from a theoreticalvalue of the heating capacity which would occur in the case of a uniformtransmission of heat into the fuel. To prevent evaporation, the heatingcapacity can then be reduced, for example, at least by an amount whichcauses the measured heating capacity to be again within apredeterminable range of the theoretical heating capacity.

In a simple way, in order to determine the boiling point, in particularthe temperature of the filter element can be measured, at leastindirectly, since the evaporation of the fuel is associated with rapidor sudden temperature rise of the filter element. A lowering of thetemperature by several degrees was observed experimentally at theboiling point of the fuel.

By means of each of these simple measures, the fuel can be heated,regardless of its respective composition, up to or just before itsboiling point, as a result of which, in particular, pollutant emissionduring a cold-starting phase is permanently improved.

Since the boiling point of the fuel used depends on its composition orquality, the pressure and the temperature, etc., this is particularlyadvantageous, since heating, of course, takes place solely to, at most,the actual boiling point of the fuel flowing through the filter elementat a given time.

Furthermore, by means of the filter element according to the invention,in particular by a comparison with predetermined calibrating curves, forexample, the following variables can also be determined:

-   I) the fuel flow in relation to the cooling of the filter element    during the throughflow of fuel,-   II) the fuel quality by determining the boiling point of the fuel,    and-   III) the pressure in the fuel system by means of a pressure    displacement of the boiling point.

By means of the filter element according to the invention in theinjection valve, in addition to the behaviour during cold starting beingoptimized, improvements can also be achieved in use during normaloperation.

Thus, in particular, in a direct-injection petrol engine, a check ofmixture formation in the combustion space, for example by controllingthe depth of penetration of the fuel, that is to say controlledvariation or keeping it constant in the case of different fuelcompositions, is of substantial interest.

The heating or overheating of the pressurized fuel in the injectionvalve allows an explosive atomization of the fuel in the event of apressure drop; that is to say during the opening of the needle of theinjection valve.

Thus, the thermal control of fuel made possible by the invention has thesame effects in terms of jet pattern and depth of penetration as othersolutions of substantially more complicated design, such as, forexample, electrostatic droplet-influencing devices or mechanicallyadjustable swirl plates in the vicinity of the valve orifice.

Further expedient refinements may be found in the subclaims. Moreover,the invention is explained in more detail with reference to exemplaryembodiments illustrated in the drawings.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a detail of a cross section through an injection valveconstructed according to a preferred embodiment of the presentinvention;

FIG. 2 shows the start of a structurally etched filter element for usewith the invention with an aspect ratio greater than 10:1;

FIG. 3 shows an enlargement of a filter element for use with theinvention; and

FIG. 4 shows a stacked structure of a filter element for use withinvention composed of a plurality of semiconductor wafers.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a detail of an injection valve 1 in cross section,the detail showing the discharge-side end region of the injection valve1. The injection valve 1 has a housing 2, into which an insert 6 ispushed on the discharge side.

The insert 6 has a seal 4 on its casing. A frustoconical outflow orifice5 for the fuel is introduced into the insert 6 on the discharge-side endface. Arranged on the opposite (inflow-side) end face is a valve seat,on which a valve needle 9 of the injection valve 1 can be laid in aseal-forming fashion.

Furthermore, the remaining surface of the inflow-side end face of theinsert 6 is shaped in such a way that it has a termination with as low aflow resistance as possible for the fuel inflow duct 8 arrangedconcentrically around the valve needle 9.

A filter element 10 is arranged in the inflow duct 8, likewiseconcentrically around the valve needle 9. The filter element 10 issupported on the outflow side by a perforated plate 11, preferably madefrom metal.

The filter element 10 is manufactured from a semiconducting material,preferably from silicon. The ducts 3 for the fuel flowing through areintroduced in a simple and cost-effective way by means of one or moreetching methods known from semiconductor technology, such as anisotropicetching.

In order to heat the filter element 10, the latter is supplied withcurrent from outside via a line 7. In this case, it is expedient toconnect the line 7 to the positive pole and the filter element 10directly to electrical ground via the housing 2 of the injection valve1.

FIG. 2 illustrates a microscopic photograph of a filter element, thestructure of which is not yet ready-etched fully. A three-dimensionalimage of a completely etched filter element is illustrated in FIG. 3.The aspect ratio, that is to say the quotient, of half the web width tothe corresponding web length is greater than 1:10 here.

It is also clear, inter alia, from FIGS. 2 and 3 that the walls of theducts themselves are virtually smooth in this enlargement. This could,inter alia, be a reason for the low flow resistance and therefore forthe good pressure stability of the filter element.

FIG. 4 illustrates a filter element 10′ which is formed from a pluralityof semiconductor boards 12. The individual semiconductor boards 12 arearranged in alignment one behind the other in the direction of flow ofthe fuel.

The individual semiconductor boards 12 all have the ducts illustrated inFIGS. 2 and 3. In order to reduce the flow resistance, the ducts areexpediently likewise oriented in alignment one behind the other in thedirection of flow of the fuel.

The semiconductor boards 12 have, at their center, a drilled hole 17which serves for leading through the valve needle 9. Each semiconductorboard 12 has, on its inner wall facing the valve needle 9, anelectrically insulating valve-needle guide ring 18. The valve-needleguide rings 18 expediently seal off the valve needle 9 fluidically inrelation to the semiconductor boards 12.

The semiconductor boards 12 are both surrounded, along the edge, by aring-like filter housing 13 which, on the one hand, holds thesemiconductor boards 12 together and at the same time insulates themthermally in relation to the housing 2 of the injection valve 1.

Furthermore, each semiconductor board 12 has a closed insulating ring 14arranged along the edge. An insulating ring 14 is manufactured from anelectrically insulating material and engages in a C-shaped manner aroundthe edge of a semiconductor wafer 12.

The insulating ring 14 is advantageous, in particular, because less oreven no liquid flows through in the edge region of a semiconductor board12, so that, without the insulating ring 14, the edge region of thissemiconductor board 12 could heat up excessively. However, due toexcessive heating, the resistance in this region would fall, with theresult that the current required for heating would then flow out throughthe edge region.

The surfaces of an insulating ring 14 which face away from the end facesof the semiconductor boards 12, which are round here, are coated with ametallic conductor, preferably aluminum. That surface of a semiconductorboard 12 which is located outside an insulating ring 14 is likewisecoated correspondingly. The metallic coating of an insulating ring 14and the coating of the surface of a semiconductor board 12 together forma closed conductor layer 15. By contrast, the outer surfaces of theinsulating rings 15 do not have any electrically conductive coating.

By virtue of this design, it is possible to conduct a heating currentthrough a semiconductor board 12 and thereby heat the latter in acontrolled manner. The heating current is conveyed through asemiconductor board 12 preferably in a controlled way.

To form electrical contact with the filter element 10, the positive poleis expediently applied directly to one of the two outer, that is to sayend-face conductor layers 15, while the other corresponding outerconductor layer 15 is connected to the housing 2 of the injection valve1, and consequently to electrical ground, if appropriate via or with theinterposition of an electrical leadthrough ring 16 described later. Inthis way it is possible, for example, to have, inter alia, a simpleembodiment of an injection valve of this type.

By virtue of the current, which can be conveyed in a controllable mannerthrough the semiconductor boards 12, or of the applied voltage, it ispossible that the heating of the semiconductor wafers 12 andconsequently of the liquid, preferably fuel, flowing through can becontrolled quantitatively. As a result of this controlled heating of theliquid, the fuel can at any time be conditioned in terms of itstemperature within the limits predetermined by the system. Improvedthermal conditioning gives rise, in turn, to better exhaust-gasbehaviour, in particular during the cold-starting phase of an engine.

As already mentioned, a leadthrough ring 16 is also arranged on one endface of the filter element 10 and between two semiconductor boards 12.The leadthrough ring 16 is manufactured from an electrically conductivematerial. The leadthrough rings 16 arranged between two semiconductorboards 12 serve for connecting two semiconductor boards 12 electricallyto one another. In the present case, the leadthrough ring 16 arranged onthe end face of the filter element 10 serves for the electricalconnection of the corresponding outer semiconductor board 12 toelectrical earth.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. Method for producing a filter element for an injection valve of aninternal combustion engine comprising: selecting a nonporoussemiconductor material for the filter element; and forming linearparallel longitudinally extending fluid flow ducts through thesemiconductor material.
 2. Method according to claim 1, wherein theducts are etched anisotropically.
 3. Method according to claim 1,wherein the semiconductor selected is silicon.
 4. Method according toclaim 1, wherein the step of forming linear ducts in the semiconductorincludes forming longitudinal ducts extending between upstream anddownstream surfaces of the filter element.
 5. Method of producing afilter element arranged inside an injection valve of an internalcombustion engine, comprising: selecting a nonporous material for thefilter element; forming linear parallel longitudinally extending ductsthrough said nonporous material, said ducts extending between upstreamand downstream surfaces of the filter element; and providing heatingmeans for heating regions of walls of the ducts along a longitudinalextent of the walls.
 6. Method according to claim 5, further comprisingmaking the filter element at least partially from a semiconductingmaterial at least in a vicinity of fuel flow.
 7. Method according toclaim 6, wherein the semiconducting material includes silicon.
 8. Methodaccording to claim 6, wherein the semiconducting material includesconductive aluminum metal.
 9. Method according to claim 5, furthercomprising installing a perforated stabilizing plate, through which fuelcan flow, wherein: said stabilizing plate is made from a metal; and saidstabilizing plate is arranged on an outflow side of the filter element.10. Method according to claim 5, further comprising: forming said filterelement with a plurality of semiconductor plates arranged one behind theother; and providing the semiconductor boards with said linearlongitudinal ducts.
 11. Method according to claim 5, further comprisingthermally insulating the filter element in relation to a housing of theinjection valve.
 12. The method according to claim 1, furthercomprising: forming said filter element with a central opening having asize which is selected to accommodate and contact a valve needle of saidinjection valve.
 13. The method according to claim 12, furthercomprising: forming said filter element with a perimeter having a sizeand shape which are selected to correspond to a size and shape of a fuelinflow duct of said injection valve.
 14. The method according to claim5, further comprising: forming said filter element with a centralopening having a size which is selected to accommodate and contact avalve needle of said injection valve.
 15. The method according to claim14, further comprising: forming said filter element with a perimeterhaving a size and shape which are selected to correspond to a size andshape of a fuel inflow duct of said injection valve.
 16. The methodaccording to claim 1, wherein said semiconductor is monocrystallinesilicon.